Philippi granitoid as a proxy for the Oligocene and Miocene crustal deformation in the Rhodope Massif (Eastern Macedonia, Greece)

Tranos, Markos D.; Eleftheriadis, Georgios E.; Kilias, Adamantios A.

Abstract

Philippi granitoid is a small body of quartz diorite to quartz monzodiorite composition that has few aplite veins and abundant microgranitoid enclaves. This granitoid has intruded into the Pangeon Unit of the Rhodope massif (Hellenic hinterland) and reveals contact metamorphism, but no discernible crystal-plastic deformation. New Ar-dating constrains its emplacement around the Middle Oligocene (≈ 30 Ma) and suggests approximately 30 °C/My cooling rate during the Late Oligocene. Strain analysis of the microgranitoid enclaves using the Rf/φ technique and the study of the faulting affecting the granitoid allow us to suggest that (a) The Philippi granitoid intruded into the Pangeon Unit through a steeply dipping conduit that trends along the axial plane of dominant NE-SW open buckle folds. The latter which were formed due to a NW-SE compression (D2 event), have refolded older Tertiary isoclinal and recumbent folds (D1 event); (b) Around 30 Ma, it was emplaced in the upper crust (<15 km) at a S-shaped bend zone formed due to inhomogeneous folding progression, which however, cannot be recognised on the non magmatic (or solid-state) flow of the granitoid; (c) In the Early Miocene, the granitoid was deformed by strike-slip faults driven by a transtension - strike-slip stress regime (D3 event) the greatest principal stress axis of which, trends NNW-SSE (similar orientation with the D2 event); (d) During the Middle Miocene the faulting deformation progressively changed to oblique NW-SE pure extension (D4 event), (e) The last deformation (D5 event) was a NE-SW radial extension activating normal faults since the Late Miocene. The fact that the Philippi granitoid is exposed few kilometers away from the large Kavala granitoid that was also emplaced into the Pangeon Unit, but in deeper crustal levels in the Early Miocene, raises questions about the proposed models which mainly suggest that the late-orogenic processes of the Hellenic hinterland were simply dominated by a NE-SW extension and low-angle extensional detachments ignoring other possible late orogenic processes such as those related to the transpression tectonics and large nearby structures namely, the 120-km-long Kavala-Xanthi-Komotini fault.